WebXR depth: fix data type mismatch between spec/idl and implementation

Bug: 1189518
Change-Id: Iaa5bf1b3dc905015b5c5ab1bba2df0a7c54671bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2774679
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Piotr Bialecki <bialpio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#864702}
diff --git a/webxr/depth-sensing/cpu/depth_sensing_cpu_luminance_alpha_dataValid.https.html b/webxr/depth-sensing/cpu/depth_sensing_cpu_luminance_alpha_dataValid.https.html
index 3bda9e2..db88c42 100644
--- a/webxr/depth-sensing/cpu/depth_sensing_cpu_luminance_alpha_dataValid.https.html
+++ b/webxr/depth-sensing/cpu/depth_sensing_cpu_luminance_alpha_dataValid.https.html
@@ -37,6 +37,10 @@
 }
 
 const assert_depth_valid = function(depthInformation) {
+
+  assert_true(depthInformation.data instanceof ArrayBuffer,
+              "XRCpuDepthInformation.data must be of type `ArrayBuffer`!");
+
   for(let row = 0; row < depthInformation.height; row++) {
     for(let column = 0; column < depthInformation.width; column++) {
       // middle of the pixel: